This invention relates to a method of characterizing the occupant of a motor vehicle seat for purposes of allowing or suppressing air bag deployment based on sensed occupant weight, and more particularly to a method of distinguishing an empty seat from a seat having an object placed on it.
Vehicle occupant weight detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of characterizing the occupant for purposes of determining whether to allow or suppress deployment of the restraints. For example, it is generally desired to allow deployment for a child or small adult, and to suppress deployment (or reduce deployment force) for a small child. In the case of infant or child seats (referred to herein collectively as child seats) that are placed on the vehicle seat and cinched down with a seat belt, it is generally believed that deployment should be suppressed entirely.
As disclosed in U.S. Pat. No. 6,247,936 issued on Jun. 12, 2001 and assigned to the assignee of the present invention, a tightly cinched child seat can be distinguished from a small adult (such as a 5th percentile adult female) by detecting the variation in the sensed weight during vehicle movement. The occupant is characterized as a child or small adult if the variation exceeds a threshold, whereas the occupant is characterized as a child seat if the variation is below the threshold, as a tightly cinched seat belt severely restricts variance. And as disclosed in U.S. patent application Ser. No. 09/895,742 filed on Jul. 20, 2001, and assigned to the assigned to the assignee of the present invention, detected pressure variations due to operating the vehicle on a rough road surface are minimized by normalizing the detected pressure variation for fluctuations in vertical acceleration of the vehicle during vehicle movement.
An issue that is not addressed in the above-mentioned patent applications, however, concerns distinguishing between an empty seat and a seat having a small object placed on it. Although the detected pressure may initially resemble an empty seat due to the low indicated weight, variation of the detected pressure during the ensuing vehicle operation can lead the system to conclude that the seat is occupied by a small unrestrained child. In a worst case condition, the system can oscillate between the two characterizations. Although deployment of the inflatable restraints will be suppressed in either event (empty seat or small child), it is important to know when the seat is truly empty for purposes of adaptive calibration. Additionally, in applications where the occupant characterization and suppression status are displayed for driver verification of proper system operation, it is confusing for the displayed status to repeatedly shift between messages indicating empty seat and child occupant. Accordingly, what is needed is a method of more accurately distinguishing between an empty seat and a seat having a small object on it, and for displaying a consistent status message to the driver of the vehicle.
The present invention is directed to an improved weight-based occupant characterization method that reliably distinguishes between an empty seat and a seat having a small object on it. According to the invention, the seat occupancy is characterized using primary and secondary classification methodologies depending on the vehicle operation. The primary classification methodology is initiated prior to vehicle movement, and characterizes the seat occupant based on measured seat pressure. If deployment of the restraint is suppressed due to the characterization of the primary classification methodology, the seat occupancy is characterized by a secondary classification methodology based on variation of the measured pressure once the vehicle is in motion. Once the secondary classification methodology has characterized the seat occupancy, the characterization of the primary classification methodology is discarded in favor of the characterization of the secondary classification methodology.